Pneumatically operated toilets are commonly found in railroad cars, cruise ships, airplanes and the like, where the space and/or water constraints render conventional flush toilets impractical. A typical pneumatically operated toilet includes a bowl with a waste opening proximate the bottom thereof and a water inlet near the rim. The waste opening communicates with a waste transfer chamber thereunder and is selectively closed and opened by a flapper valve. The waste transfer chamber connects to an evacuation line, via which waste and water are removed from the waste transfer chamber by air pressure. The flapper valve and a water inlet valve are typically also pneumatically operated.
In typical operation, in a “ready-for-use” state, the waste transfer chamber is depressurized and empty, the flapper valve is closed, and a small amount of water is held in the basin. After use, in response to user operation of a flush button or lever, the flapper valve is opened and additional water is introduced via the water inlet to transfer waste into the waste transfer chamber. After flapper valve is closed, water flow is stopped after the small amount of water normally retained in the bowl is reintroduced. The waste transfer chamber is pressurized to impel the waste and water out via the evacuation line.
Conventionally, all of these operations (i.e., control of the water inlet, the movement of the flapper valve, and the pressurization of the waste transfer chamber) are controlled by a single, pneumatically-operated spool valve. An example of this valve can be seen in U.S. Pat. No. 3,968,526, the contents of which are herein incorporated by reference in their entirety. While this type of spool valve control has proven useful, further improvements are possible.